This invention relates generally to surveying equipment and more particularly to surveying equipment having lightweight and yet robust, precision construction.
Surveying equipment and particularly the support structure therefore must be able to withstand all kinds of environmental conditions while retaining its integrity and dimensional accuracy. In many instances, the dimensional accuracy is imperative in order to obtain the correct measurements in a geographic survey. For instance, prism poles and global positioning satellite (GPS) poles must be able to retain a substantially fixed position of extension as they are moved from place to place over uneven terrain and in all kinds of weather. Prism poles include two or more interfitting pole sections, and support a prism or other measurement device at the top used to sight or determine positions with laser, modulated infrared, angular and/or GPS position locators or like surveying systems. The prism reflects light back to the position locator for determining the location of the prism at different locations in a survey. The prism pole may be constructed with telescoping sections so that it may be collapsed to a reduced height (e.g., about four feet) for storage and transport, and then extended to its operating height which may be, typically, eight feet or more. In topological surveys, it is important that the pole be able to maintain its extended height as it is moved from place to place. It is therefore, critical to be able to lock the pole sections in a fixed position of extension in such a way as to have them stay. Moreover, the pole must maintain its longitudinal axis as it is extended so that its extended height is accurate every time. Similarly, the pole must be able to withstand numerous cycles of extension and retraction, and frequent rough handling while maintaining this accuracy. Still further, it is frequently desirable to completely detach the telescoping sections without substantial disassembly of the surveying pole or loss of accuracy upon reassembly.
The need for durability and accuracy has traditionally led to making surveying poles out of metal. However, metal poles can expand and contract significantly with changes in the temperature of the surrounding environment which is detrimental to accuracy of the survey. Metal poles are also capable of plastic deformation which can lead to inaccurate measurements. Carrying a heavy metal pole over uneven or broken terrain, as will be frequently necessary in surveying, can be very difficult and physically taxing. Using metal poles in the outdoors also presents a risk of lightening strike. It is possible to make poles out of lighter weight, non-conducting material, such as fiberglass, which are sturdy and weather-resistant. However, these poles will typically not withstand the clamping forces conventionally applied to metal poles to hold them in a fixed extension. Lower clamping forces may not adequately hold the pole sections in position. A similar problem is present when attaching something which must maintain a precise orientation, such as a level, to the pole. Non-metal materials may also be less likely to withstand impact forces associated with forcefully retracting the pole sections.
The surveying poles or other surveying equipment support structure may have telescoping sections, screw-together sections or a combination of the two. It is important to be able to rapidly collapse the poles for storage and transport. Also for cleaning in the field, the pole sections need to be able to be quickly and accurately disassembled and reassembled. Regardless of the material of the pole, it is often difficult to economically manufacture the pole sections so that they will maintain the same linear axis every time they are screwed together. One problem is the initial installation of screw fittings in ends of the pole sections. Care must be taken to achieve axial alignment upon installation. Another problem is the accumulation of debris on the fittings so that when screwed together, the fittings do not achieve face-to-face engagement which results in axial misalignment of the pole sections. For telescopingly interfitted pole sections, it is important to be able to easily disassociate the sections for cleaning or repair, and reassemble them while maintaining accuracy.
It is also not uncommon for these poles to have some accessory equipment. For instance, the bottom of a prism pole is conventionally equipped with a steel point to locate the pole on the ground. However in circumstances where the ground is soft, it is undesirable to have the point engaging the ground because the point tends to penetrate the surface of the ground. As a result, the location of the top of the pole above the ground can be inconsistent. Conventionally, the steel point has been removed and replaced with a blunt or greatly enlarged blunt end under these circumstances. The replacement involves several steps and it is necessary to carry the blunt end (or the steel point) around separately from the pole until used. The steel point can be difficult to safely carry because its point can be rather sharp.
Among the several objects and features of the present invention may be noted the provision of a lightweight surveying pole which is sturdy and weather-resistant; the provision of such a surveying pole which accurately maintains an extended height; the provision of such a surveying pole which maintains sections in a coaxial relation; the provision of such a surveying pole which can be disassembled and accurately reassembled for cleaning and repair; the provision of such a surveying pole which can be reconfigured with minimal steps; and the provision of such a surveying pole which can be efficiently manufactured with high accuracy.
Generally, a surveying pole for use in locating a position in a survey of land constructed according to the principles of the present invention comprises a first pole section and a second pole section telescopingly received in the first section for extension and retraction relative to the first section. A lock to selectively lock the second pole section in a fixed position of extension from the first pole section comprises a base mounted on the first pole section, a movable clamping jaw supported by the base, and an actuator for use in moving the jaw between a locked position in engagement with the second pole section and an unlocked position spaced from the second pole section. The movable clamping jaw comprising a rigid jaw member and an elastomeric pad mounted on the jaw member. The elastomeric pad includes an engagement surface positioned for engaging the second pole section in the locked position of the lock. At least one of the elastomeric pad and the jaw member is shaped to provide frictional resistance to relative telescoping movement between the first and second pole sections in the locked position which increases upon application of force tending to induce such relative telescoping movement.
In another aspect of the present invention, a surveying pole of the present invention generally comprises a first pole section and a second pole section telescopingly received in the first section for extension and retraction relative to the first section. A lock releasably locks the second pole section in a fixed position of extension from the first pole section. The first pole section has an internal first stop formed therein, and the second pole section having a second stop engageable with the first stop for limiting extension of the second pole section from the first pole section. At least one of the first and second stops being resiliently deformable upon application of an axial extension force equal to or greater than a yield force for moving past each other to release the second pole section from the first pole section such that the first and second pole sections are adapted for releasable snap together connection.
In still another aspect of the present invention, a surveying pole of the present invention generally comprises a first pole section and a second pole section telescopingly received in the first section in a substantially sliding sealing relation for extension and retraction relative to the first section. A lock releasably locks the second pole section in a fixed position of extension from the first pole section. The first and second pole sections define an internal volume of the surveying pole which contracts upon retraction of the second pole section into the first pole section. At least one of the first and second pole sections being formed to release air from the volume at a controlled rate when the second pole section is retracted into the first pole section for cushioning the retraction the second pole section.
Other objects and features of the present invention will be in part apparent and in part pointed out hereinafter.